Структура макрозообентоса водотоков в бассейне Верхней Лены. Сообщение 1. Структура макрозообентоса основного русла р. Лены (на участке Жигалово – Усть-Кут)

Abstract

Lena River is one of the largest watercourses in Siberia. It is 4,400 km long with a catchment area of 2,490,000 km2. The upper section of the river begins from its source to the Vitim River mouth (1,690 km long). Studies of the current state of the macrozoobenthos of the main riverbed of Upper Lena were conducted in the section from Zhigalovo settl. to Ust-Kut sity in summer 2017, 2018 and 2021. In the studied river section was found to contain more than 24 groups of benthic invertebrates of different taxonomic ranks: Hydrozoa (hydras), Planaria (planaria), Oligochaeta (earthworms), Hirudinea (leeches), Nematoda (roundworms), Gastropoda (gastropods), Bivalvia (bivalves), Ostracoda (seed shrimps), Amphipoda (freshwater shrimps), Ephemeroptera (mayflies), Plecoptera (stoneflies), Odonata (dragonflies), Megaloptera (alderflies), Trichoptera (caddisflies), Acariformes (water mites), Corixidae and other Heteroptera (true bugs), Dytiscidae (diving beetles), Chironomidae (chironomids), Ceratopogonidae (biting midges), Dolichopodidae (longlegged flies), Psychodidae (drain flies), Tipulidae (crane flies), Limoniidae (limoniid crane flies), Stratiomyidae (soldier flies) and other dipterans. The highest number of taxonomic groups of benthic animals is found on coarse gravel substrates with moss, chara or eleocharis (23 groups). The lowest diversity was found on clean gravels (9 groups). For the main riverbed of Upper Lena there is considerable heterogeneity in the distribution of both the main zoobenthos taxonomic groups and quantitative indicators (abundance and biomass). Mean values of zoobenthos number and biomass varied within a wide range: on gravel substrates from 784 to 17.296 individuals/m–2 in abundance and from 1.104 to 24.416 g/m–2 in biomass, on silty substrates from 3.650 to 74.783 individuals/m-2 and from 2.48 to 107.07 g/m–2, respectively. The larvae of chironomids, mayflies and oligochaetes are the main component of the macrozoobenthos structure of the Upper Lena, with the larvae of stoneflies and caddisflies playing a secondary role. On gravel substrates the structure-forming element in terms of numbers and biomass is the larvae of chironomids and mayflies, and much less frequently bivalves. In silty substrates the larvae of chironomids, oligochaetes and leeches are most important, in some areas the larvae of mayflies Ephemera orientalis or Gammarus lacustris are of primary importance.